1. Field of the Invention
The present invention relates to a method of providing survey data using a surveying instrument, means for performing the method and a corresponding surveying instrument.
2. Brief Description of the Related Art
Surveying often includes determination of angles or of positions of points, e.g. reflectors (triple reflectors) or targets in the terrain. Those angles or positions may be measured by surveying instruments such as theodolites or tacheometers.
Positions in space can be defined by coordinates in a suitable coordinate system. For example, the position of a point may be defined by its Cartesian coordinates which are defined with respect to a Cartesian coordinate system having three axes which are orthogonal to each other. For measuring positions, however, spherical coordinates are more appropriate. As shown in FIG. 1, the position of a point P may be defined in spherical coordinates by its distance d to the origin of an orthogonal coordinate system, an angle α between one of the horizontal axes of the coordinate system and a line connecting the origin of the coordinate system with a projection of the point P onto the horizontal plane and finally a vertical angle θ between the coordinate system axis orthogonal to the horizontal plane and a line connecting the origin of the coordinate system and the point. As well known in the art, Cartesian coordinates can be transformed into spherical coordinates and vice versa.
Surveying instruments such as theodolites or tacheometers, also known as tachymeters or total stations, make use of spherical coordinates. As schematically shown in FIG. 1, known theodolites or tacheometers comprise a telescope 1 which is rotatable about a vertical axis 2 which is fixed to a base element 3 of the theodolite or tacheometer and a tilting axis 4, also termed horizontal axis, which is rotated with rotation of a telescope 1 about the vertical axis 2. Angles of rotation about the vertical axis 2 and angles of tilting about the tilting axis can read from a corresponding horizontal circle 5 and a vertical circle 6.
In an ideal tacheometer as shown in FIG. 1, the tilting axis 4 is orthogonal to the vertical axis 2 and both axes intersect in one point. Further, a line of the sight 7 of the telescope 1, also called sighting axis or sight axis, is orthogonal to the tilting axis 4 and further runs through the intersection point of the tilting axis 4 and the vertical axis 2.
For measuring the position of a point, ideally, the tacheometer is oriented such that the vertical axis 2 is perfectly perpendicular, i.e. it points in the direction of gravity. Then, a spherical coordinate system can be defined by a plane orthogonal to the vertical axis 2, the origin being the intersection point of the of the tilting axis 4 and by the vertical axis 2. By the horizontal circle 5 one axis of the coordinate system can be defined which is fixed with respect to the base element 3. For measuring the above-mentioned angles α and θ, the sighting axis 7 of a telescope 1 is directed to the point to be measured by rotating the telescope 1 about the vertical axis 2 and tilting the telescope 1 about the tilting axis 4. The angle α can than be read from the horizontal circle and the angle θ from the vertical circle 6. For measuring the distance of a target point from the instrument a tacheometer has a distance measuring unit which allows measurement of the distance of a target point sighted at from the instrument. Knowing the distance of the point from the instrument, the Cartesian coordinates can be easily obtained.
Video-tacheometers differ from traditional tacheometers in that they comprise a camera which may for example replace the whole telescope or just the eyepiece of the telescope or may be provided in addition to the telescope. As schematically shown in FIG. 2, the camera 8 comprises an optical system 9 and an image sensor 10. The optical system 9 forms images of points in a scene on the image sensor 10. A point P to be measured is thus imaged onto a certain position P′ on the image sensor 10. The image sensor 10 comprises an array of photo-detector elements 10′ which are responsive to the image formed on the sensor and produce respective detection signals.
If known tacheometers or even video-tacheometers are used to survey a target region the telescope unit has to be redirected to all points of interest in the target region separately to obtain survey data about the target region. Thus, surveying of a target region, in particular of given objects in a target region, can be quite time consuming.
It has been found that the conventional method of providing survey data and the conventional surveying instrument could still be improved to obtain survey data more rapidly and comfortably.